Your plants use three main types of plant respiration to make energy in your garden. The two main plant respiration pathways are aerobic and anaerobic. A third type is called photorespiration. Aerobic runs most of the time when oxygen is plentiful. Your plants switch to the other types when conditions change around them.
Aerobic respiration powers your plants in normal growing conditions all day long. It runs in the mitochondria where oxygen helps break down glucose to CO2 and water. This pathway makes 27 to 28 ATP from each glucose your plant burns for energy. Your leaves, stems, and roots all use this type when they have plenty of air around them.
When I first overwatered a potted fern, I noticed a sour smell from the soil after a few days. That was anaerobic respiration at work in the soggy roots below the surface. Without oxygen, my plant's roots switched to a backup mode that makes ethanol as waste. This is the same process that makes beer and wine with that same yeasty smell in your nose.
Anaerobic mode only makes 2 ATP per glucose while aerobic makes 27 or 28. Your plant can survive on this for a short time but will weaken fast if it goes on too long. The ethanol buildup can also damage root cells and kill them over time. This is why soggy soil leads to root rot in so many houseplants and garden beds all around the world.
Aerobic anaerobic respiration depends on how much oxygen your roots can get from the soil. Good soil with lots of air pockets lets roots run full aerobic mode all day long. Packed or flooded soil forces them into the weak backup mode instead. You control which type your roots use by how you water and care for your soil.
The photorespiration process is a third type that runs in bright light when CO2 runs low in the leaf. Your plant's enzyme grabs oxygen by mistake and starts a wasteful cycle that burns energy. This process makes zero ATP for your plant to use and wastes what it already made. Hot dry days make it worse because stomata close to save water and trap oxygen inside the leaf.
Photorespiration can cost your plants 25 to 50% of their fixed carbon in hot weather. This happens most when leaves heat up fast in the summer sun all around midday. Some crops like corn and sugarcane have tricks to avoid this built into their leaf cells. Most garden plants don't have these tricks and suffer in extreme heat waves.
Knowing these plant respiration pathways helps you keep your plants in aerobic mode most of the time. Give your roots loose well drained soil so they never have to switch to anaerobic backup. Water during cool morning hours in summer to help your plants avoid peak photorespiration in hot sun. Your plants will make more energy and grow better when you help them respire the right way all season long.
Read the full article: Respiration in Plants: The Complete Process Guide
